1. Field of Invention
This invention relates to a an expansible chamber engine with cam driven pistons, such as an internal combustion engine, that during operation can change expansion ratios and intake displacements and appropriately limit the fuel air charge, specifically to an arrangement that shifts combustion peaks between, differing in height, top dead center positions on a four stroke piston drive cam, by shifting the valve and combustion timing and, limits the charge to prevent pre-ignition firing that would be caused by the shift, by controlling the open duration of the intake valve. And, limits the maximum charge volume so the work used to supercharge replaces cylinder compression.
2. Description of Prior Art
Increasing the fuel efficiency or decreasing the specific fuel consumption, SFC, in commercially acceptable spark ignition engines has heretofore been restricted in many ways:
(a) Limiting is defined for this invention as the process of controlling the unthrottled fuel air charge into a cylinder by variably closing the intake valve early. The advantages for an engine with one stage of limiting is discussed in U.S. Pat. No. 4,280,451. The compression ratio, cylinder to clearance volume, was apparently increased by shaving the heads to reduce the clearance volume, but the effective cylinder intake volume was also reduced by early valve closure on the intake stroke. The resulting compression ratio, herein called the limited compression ratio, is based on the reduced effective intake volume and, is still limited by pre-ignition firing to the same maximum as before. The volumetric efficiency is decreased since only part of the cylinder volume can be filled with fuel air charge. A larger engine is required to produce the same maximum power. PA1 (b) Decreasing SFC by increasing the expansion ratio is restricted by the mechanical complexity required. Current commercial designs offer only fixed and equal expansion and compression ratios. PA1 (c) The primary means of controlling engine output currently is throttling, which restricts lowering SFC due to the inherent throttling losses. PA1 (d) Decreasing SFC by increasing the compression ratio, or more relevantly the pre-ignition pressure to atmospheric pressure ratio, is restricted by the maximum pre-ignition pressure and temperature that can be used and still prevent pre-ignition firing. PA1 (e) The displacement of most engines is fixed. There have been recent attempts to decrease SFC by reducing displacement during operation. This has been done by deactivating the valves and switching off some cylinders. Unfortunately the cylinder cools, increasing wear and decreasing combustion efficiency when restarted. The system has not been commercially successful. PA1 (f) Automotive engines in urban and suburban areas spend most of the time at half throttle or less, operating at 10 to 20 percent of maximum power output. Unfortunately total engine efficiency is sensitive to reductions in load. Current engines, which have their lowest SFC when fully loaded, operate most of the time lightly loaded, in their worst SFC region. PA1 (g) Controlling engines by limiting produces a higher hydrocarbon content in the waste gas than does throttling. Specifically in the idle and lower partial load regions, as discussed in U.S. Pat. No. 4,765,288. Briefly, after valve closure, the charge expands to fill the full cylinder and then is recompressed into the clearance volume. This expansion cools the charge mixture, albeit only momentarily, until the charge is recompressed to the original volume that occured when the valve closed. The theory stated is that "the fuel cools relatively too much, the fuel evaporates poorly and as a result poor mixture preparation takes place" causing the higher hydrocarbon level. The proposed solution was to restrict the valve opening for an extended period of time. In effect, using the valve as a throttle, partially defeating one of the main purposes of limiting. The elimination of throttling losses. PA1 (h) Controlling valve closure by hydraulic means is not new. One method is disclosed in U.S. Pat. No. 4,466,390. Valve operation occurs as a translating fluid plug, interposed between a camshaft and a valve, is collapsed and refilled. This system requires a hydraulic system with sufficient capacity and piping to rapidly refill the fluid plug, an electronic system to sense, compute, amplify and send a sufficiently powerful signal to actuate the fluid release valve each time the cylinder valve operates, and a fluid release valve that operates each time the cylinder valve operates. A complex and costly system. PA1 (i) Supercharging is common practice since it produces more power from a smaller package. However, any practical potential for lowering SFC is due to increasing the mechanical efficiency, not to recovering additional work. Particularly so in engines that must operate over a wide range of conditions. The problem is that compression from the supercharger adds to the compression in the cylinder, and the total compression is still limited by the pre-ignition firing characteristics of the fuel. In the crossover speed ranges where the cylinder would have been filled without supercharging and yet there is substantial supercharging, the cylinder compression ratio must be kept low enough to avoid pre-ignition firing. At relatively lower speeds with little to no supercharger output, the total compression ratio is just the cylinder ratio. Thus at part load an engine of this type operates at a lower compression ratio, increasing the SFC for these operating conditions. Compensating for supercharger output by early intake valve closure was disclosed in Deutsche Patentschrift DT-PS 100 1049. It has been adapted to large diesels and gas engines, such as 2500 horsepower. These engines are primarily for steady state power production and as such are not suitable for automotive use. Indeed, the literature teaches that spark ignition engines do not need variable timing. Engines of this type have reduced pre-ignition temperatures and pressures at light loads, contributing to poor combustion. And, the lower pressures result in lower pressure ratios and lower cycle efficiency. The method is known, but the expense and complexity of the mechanical requirements to vary the valve timing further discourages commercial use in other than stationary or marine engines. PA1 (k) In throttled engines the high vacuum that occurs during deceleration causes rapid evaporation of liquid fuel from the intake manifold walls. The resulting rich mixture increases exhaust emissions of carbon monoxide CO and hydrocarbons HC and also creates a potentially explosive vapor in the exhaust manifold if injected air is present. PA1 (l) The high temperatures during the combustion process produces nitrous oxides NO.sub.x. Large and expensive catlytic reactors are used to reduce the level of these emissions. PA1 (m) The maximum torque from an engine occurs when the cylinders are fully charged or loaded and, when the compression ratio is at the maximum allowed to avoid pre-ignition firing. The addition of supercharging increases the mechanical efficiency and relatively lowers the expansion ratio. But, does not substantially increase the torque per unit displacement, since the effective displacement is increased by adding the supercharger. This is easier to see when considering a piston supercharger instead of a turbo-charger. The true displacement is that of the supercharger. Except for the effects of a slight increase in mechanical efficiency, torque per unit of true displacement is not increased. PA1 (a) To operate an IC engine at maximum prior art volumetric efficiency and have the capability to shift, within the same maximum displacement, to a more fuel efficient cycle. PA1 (b) To decrease SFC by utilizing a greater expansion ratio cycle. PA1 (c) To provide a commercially acceptable system to control engine output by varible intake valve closure, eliminating or substantially reducing throttling losses. PA1 (d) To decrease SFC by increasing the pre-ignition pressure, or pressure ration with respect to atmospheric pressure, for part load operation. PA1 (e) To provide a system that effectively reduces engine displacement without shutting off cylinders. PA1 (f) To modify engine operation such that for part load operation the SFC is lower than for full load operation. PA1 (g) To change the pre-ignition conditions when limiting to improve combustion and eliminate or substantially reduce the higher hydrocarbon level. PA1 (h) To provide a reliable and relatively low cost hydro-mechanical valve arrangement, that reduces the hydraulic flow rate required to operate the valve and further, to provide a system that needs only passive control, either on or off, for steady state operation. No timed signal required for each valve cycle. PA1 (I) To enable the feedback of supercharger compression work into the engine, replacing instead of adding to cylinder compression work. PA1 (k) To reduce and possibly eliminate the CO and HC emissions that comes from the excessively rich mixture produced by high manifold vacuum during deceleration and idle. PA1 (l) To reduce NO.sub.x emissions by increasing the burned gas mass fraction during combustion. PA1 (m) To increase the torque per unit of true displacement by enabling supercharger compression to replace cylinder compression and maintaining or increasing the expansion ratio at part load.